This invention relates generally to an internal combustion engine and, more particularly, to a two turbocharger engine emission control system for an internal combustion engine.
An exhaust gas recirculation (EGR) system is used for controlling the generation of undesirable pollutant gases and particulate matter in the operation of internal combustion engines. Such systems have proven particularly useful in internal combustion engines used in motor vehicles such as passenger cars, light duty trucks, and other on-road motor equipment. EGR systems primarily recirculate the exhaust gas by-products into the intake air supply of the internal combustion engine. The exhaust gas which is introduced to the engine cylinder reduces the concentration of oxygen therein, which is turn lowers the maximum combustion temperature within the cylinder and slows the chemical reaction of the combustion process, decreasing the formation of nitrous oxides (NOx). Furthermore, the exhaust gases typically contain unburned hydrocarbons which are burned on reintroduction into the engine cylinder, which further reduces the emission of exhaust gas by-products which would be emitted as undesirable pollutants from the internal combustion engine.
In many EGR applications, the exhaust gas is diverted by a poppet-type EGR valve directly from the exhaust manifold. The percentage of the total exhaust flow which is diverted for reintroduction into the intake manifold of an internal combustion engine is known as the EGR flow rate of the engine.
Some internal combustion engines include turbochargers to increase engine performance, and are available in a variety of configurations. For example, fixed housing turbochargers have a fixed exhaust inlet nozzle which accelerates exhaust gas towards a turbine wheel, which in turn rotates a compressor. Also, a variable nozzle turbocharger (VNT) has a variable nozzle having a ring of a plurality of variable vanes which are controlled to change the cross sectional area through which the exhaust gases pass to reach the turbine. In a VNT, the smaller the nozzle opening, the faster the gas velocity to the turbine, and in turn, the higher the boost. Still further, it is known to provide a turbocharger having two independent compressors, which is known as a double sided compressor. Use of a single turbocharger of the types described above, however, constrain the operation and configuration of an EGR system for use with an internal combustion engine.
When utilizing EGR in a turbocharged diesel engine, the exhaust gas to be recirculated is often removed upstream of the exhaust gas driven turbine associated with the turbocharger. The recirculated exhaust gas is typically introduced to the intake air stream downstream of the compressor and air-to-air after-cooler (ATAAC). Reintroducing the exhaust gas downstream of the compressor and ATAAC is preferred in some systems due to the reliability and maintainability concerns that arise if the exhaust gas passes through the compressor and ATAAC.
In other systems, such as a system having a double sided turbocharger, a gas flow from an EGR valve may be directed to a secondary compressor inlet of the turbocharger. A separate EGR cooler is provided upstream of a secondary compressor inlet to cool the EGR gas prior to being received by the secondary compressor. In addition, a bypass circuit may be provided around the EGR cooler to adjust the amount of cooling of the EGR gas by the EGR cooler. Such a system, however, is subject to the negative effects of condensation and associated corrosion.
The present invention is directed to overcoming one or more of the problems or disadvantages associated with the prior art.
In one aspect of the invention, an internal combustion engine is provided comprising a block defining a plurality of combustion cylinders, the plurality of combustion cylinders having at least a first group of combustion cylinders and a second group of combustion cylinders. A first exhaust manifold is connected to the first group of combustion cylinders to receive first combustion gases from the first group of combustion cylinders. A second exhaust manifold is connected to the second group of combustion cylinders to receive second combustion gases from the second group of combustion cylinders. A first turbocharger is provided having a first turbine and a first compressor, the first turbine having a first gas inlet port and a first gas outlet port, the first compressor having a first air inlet port and a first air outlet port, the first gas inlet port being connected in fluid communication with the first exhaust manifold, and the first air inlet port of the first compressor being in fluid communication with the atmosphere. A second turbocharger is provided having a second turbine and a second compressor, the second turbine having a second gas inlet port and a second gas outlet port, the second compressor having a second air inlet port and a second air outlet port, the second gas inlet port being connected in fluid communication with the second exhaust manifold to receive at least a portion of the second combustion gases, the second gas outlet port being connected in fluid communication with the first gas inlet port of the first turbine, and the second air inlet port of the second compressor being in fluid communication with the first air outlet port of the first compressor. A mixer is provided having a first input port, a second input port and an output port, the first input port being coupled to the second air outlet port to receive compressed air from the second turbocharger, and the output port being in fluid communication with the plurality of combustion cylinders. A valve is connected in fluid communication with the second exhaust manifold to receive a remainder of exhaust gases not included in the at least a portion of the combustion exhaust gases received by the second turbine, the valve being connected in fluid communication with the second input port of the mixer to deliver at least a portion of the remainder of exhaust gases to the mixer for mixing with the compressed air in the mixer.
In another aspect of the invention, a method of providing engine emission control for an internal combustion engine is provided, comprising the steps of: providing a first turbocharger having a first turbine and a first compressor, the first turbine having a first gas inlet port and a first gas outlet port, the first compressor having a first air inlet port and a first air outlet port; providing a second turbocharger having a second turbine and a second compressor, the second turbine having a second gas inlet port and a second gas outlet port, the second compressor having a second air inlet port and a second air outlet port; supplying first combustion gases from a first group of combustion cylinders to a first exhaust manifold; supplying second combustion gases from a second group of combustion cylinders to a second exhaust manifold; supplying the first combustion gases from the first exhaust manifold to the first gas inlet port of the first turbine; supplying at least a portion of the second combustion gases from the second manifold to the second gas inlet port of the second turbine; supplying exhaust gases expelled from the second gas outlet port of the second turbine to the first gas inlet port of the first turbine; supplying fresh air to the first air inlet port of the first compressor from the atmosphere; compressing the fresh air by the first compressor to form first stage compressed air; supplying the first stage compressed air from the first compressor to the second air inlet port of the second compressor; compressing the first stage compressed air with the second compressor to form second stage compressed air; supplying the second stage compressed air to a mixer; and supplying to the mixer at least a portion of a reminder of exhaust gases not included in the at least a portion of the second combustion gases supplied to the second turbine, for mixing with the second stage compressed air to form a mixture.